β-glucan is a polysaccharide which is composed of D-glucose as a constituent saccharide. For example, β-1,3-glucan is a polysaccharide composed of polymerized cyclic β-pyranose D-glucose molecules in which cyclic β-pyranose D-glucose molecules are bound to each other to condense via β-1,3-glucoside bonds between a hydroxyl moiety binding to a carbon atom at position 1 in a glucose molecule and a hydroxyl moiety binding to a carbon atom at position 3 in another glucose molecule. Various types of the polysaccharides such as β-glucan can be found in organisms in nature as storage molecules of saccharide that is an energy source and as structural molecules of cell walls or the like. The β-glucan contained in mushroom such as agaricus mushroom (Agaricus brazei) reishi mushroom (Ganoderma lucidum), Grifola frondosa, and Lentinula edodes is known to have various physiological activities for maintaining or promoting health. There have been made a number of attempts to utilize the β-glucan as a functional material, a pharmaceutical product, and the like which are intended for an immunopotentiating action, an anti-tumor activity, a cancer cell proliferation suppressing action, an antiallergic action, an antiinflammatory action, a cholesterol reducing action, an antithrombotic action, an action of dietary fiber, an antihypertensive action, an antidiabetic action, an improvement of hepatic function, or the like. In addition, the β-glucan is attracting expectations to be a polysaccharide functional material which can be expected to be applied to a wide spectrum of applications such as antiflatulents for preventing or relieving constipation since the β-glucan is indigestible, and cosmetics which utilize moisture retention properties of the β-glucan.
As β-glucan having beneficial activities, there is well known β-1,3-1,6-glucan having a main chain composed of β-1,3-glucoside bonds and a side chain of D-glucose from a carbon atom at position 6. The branching structure is thought to be necessary for the activities, but the mechanism of the action has not been fully clarified. In addition, β-glucan is a high-molecular weight polymer obtained from a natural substance. Therefore, the structure of β-glucan, such as a degree of branching the length of the main chain, the length of the side chain, or the like, and the presence or absence of and the degree of modification of a D-glucose hydroxyl group by amination, phosphorylation, methylation, acetylation, or the like are not uniform. The principle regarding the effects of the structure and chemical modification on the activities have not been presented. Thus, the β-glucan derived from mushroom has been preferably used only empirically in part, and there have been few attempts to utilize β-glucan derived from other organism species.
Recently, it has been found that β-1,3-1,6-glucan which is produced by a microorganism belonging to the genus Aureobasidium sp. (commonly known as “black yeast”), which is an imperfect fungi widely exist in the nature exhibits a function equivalent or superior to that of the β-glucan derived from mushroom.
For example, Patent Document 1 describes that an extracellular homopolysaccharide produced by a microorganism belonging to the genus Aureobasidium sp. is β-1,3-1,6-glucan.
In addition, Patent Document 2 describes that an Aureobasidium culture solution containing as a main component β-1,3-1,6-glucan has high antitumor activity and high immunopotentiating activity via oral administration, so the solution can be applied as a pharmaceutical product for various diseases.
Patent Document 1: JP-A-10-276740
Patent Document 2: JP-A-2002-204687